Comments

can you clarify the question or is it you have found and posted your own answer to it?
i don't think i personally can help you with this but to myself and perhaps others, it looks to be a self-answered question.
so if still needing help with this further information might allow one to see it is open and still in need of a response so it is not just passed by by misunderstanding.

its a bit of a lame tutorial provided so even with the link the question having been answered is still debatable
is there a specific section of their provided tutorial you are having trouble with if still troubled?

cometchat purchasable through phpfox is a great version also.
i still have little idea what they removed from their lowest subscription level and for chat rooms, mail and footer chat it works great for a lot less than buying from their site.

as far as i can work out from the tutorial the chat_server_key is what is entered within the IM modules admin screen within ( ACP ) phpfox administration control panel ( so you invent it? )

it appears more confusing than needed as described in the tutorial.
i have not done this process so this is untested

but try copy a random string id assume numbers and letters using - in place of spaces into both the admin panel module settings in phpfox and the config file being edited
if both are the same it may well work without further configuration ( no info could mean just that )

** this is untested **
if works try adding symbols to your key also for added security removing if that then breaks